FIX OF THE PREVIOUS EXPERIMENTAL COMMIT:

FIX OF THE PREVIOUS EXPERIMENTAL COMMIT:

Instead of serializing closures (of type status -> status), we now
serialize data. This is achieved by implementing an existential type

       NCicLibrary.Serializer(struct type status end).obj

whose semantics is "\exists 'a. 'a -> status -> status"
and by putting in the dump a list of these existential types.

The current implementation is the type-unsafe one based internally on Obj.magic.
However, the interface is (should be?) type-safe.
Other type-safe implementations could be derived by the ocaml m.l. thread on
existential types. In particular, I remember implementations via:
  - references
  - functors
  - exceptions
  - impredicative encoding via polymorphic methods

This fix allow to change the Matita code without invalidating the library.

(Critical) things still to be done:
 - decompilation
 - refreshment of URIs